Re: [PATCH] gcc/c-family/c-cppbuiltin.c: Use 20 instead of 18 for the maximized 64-bits integer decimal string length

[Chen Gang <gang dot chen dot 5i5j at gmail dot com>]

On 11/19/14 0:44, Joseph Myers wrote:
> On Sun, 16 Nov 2014, Chen Gang wrote:
> 
>> The maximize 64-bits integer decimal string length excluding NUL is 20 (
>> '-9223372036854775808'), so need use 20 instead of 18 for HOST_WIDE_INT.
>>
>> 2014-11-16  Chen Gang  <gang.chen.5i5j@gmail.com>
>>
>> 	* c-family/c-cppbuiltin.c (builtin_define_with_int_value):  Use
>> 	20 instead of 18 for the maximize 64-bits integer decimal
>> 	string length
> 
> OK.  (Though it's not a good idea to use builtin_define_with_int_value 
> with large arguments, as it won't generate any suffixes for arguments 
> outside the range of target int, and -9223372036854775808 would actually 
> need to be expressed as (-9223372036854775807LL-1).  I think it's OK that 
> it doesn't parenthesize negative numbers when outputting them - that the 
> only cases for which the lack of parentheses could affect the parse are 
> invalid for other reasons - though parentheses around negative numbers 
> output might be a good idea anyway to make it obvious the output is OK, 
> and would accord with how some macros such as __*_MIN_EXP__ are output; 
> those values should probably use builtin_define_with_int_value.)
> 

OK, thanks, what you said sounds reasonable to me. We need '(' and ')'
for negative members, and "LL" for the members which is larger than 32
bits.

For me, for simplify thinking, can let all numbers have '(', ')' and
"LL" (whether it is positive numbers or negative numbers, whether it is
large numbers or small numbers), and one sprintf() is enough:

  sprintf(buf, "%s=("HOST_WIDE_INT_PRINT_DEC")LL", macro, value);

And excuse me, I do not understand why use "(-9223372036854775807LL-1)"
instead of "(-9223372036854775808LL)": compiler will report warning for
it, but for me, it is more likely the compiler's own issue:

  bash-3.2# cat ./test.c 
  #include <stdio.h>
  
  int main ()
  {
    long long i = (-9223372036854775808LL);
    long long j = 0x8000000000000000LL;
    long long k = 0x7fffffffffffffffLL;
  
    printf("\ni: %lld, j: %lld, k: %lld\n", i, j, k);
  
    return 0;
  }
  bash-3.2# gcc -o test test.c
  test.c:5:19: warning: integer constant is larger than the largest signed integer type
    long long i = (-9223372036854775808LL);
                    ^
  1 warning generated.
  bash-3.2# ./test 
  
  i: -9223372036854775808, j: -9223372036854775808, k: 9223372036854775807



Thanks
-- 
Chen Gang

Open, share, and attitude like air, water, and life which God blessed